1. Field of the Invention
The present invention relates to medical image processing method and apparatus for processing a medical image photographed by using radiation, etc.
2. Description of a Related Art
Photography using radiation (X-ray, α-ray, β-ray, γ-ray, electron beam, ultraviolet ray and so on) is conventionally utilized in various fields, and is one of most important means for a diagnosis particularly in a medical field. An X-ray radiography is variously improved since the realization of a first X-ray radiograph, and a method using combination of a fluorescent screen and an X-ray film is a main current at present. In recent years, various digitalized devices such as an X-ray CT, an ultrasonic diagnosis and an MRI are practically used in a medical image diagnosis, and construction of diagnostic information processing systems, etc. within hospitals is going to be advanced. Many researches for the digitalization have been also made with respect to an X-ray image, and radiography using photostimulable phosphor is established and is practically used as a method to replace the conventional X-ray radiography.
Photostimulable phosphor (accumulative phosphor) is such substance that accumulates a part of radiation energy when irradiated with radiation and then generates photostimulated luminescence light in accordance with the accumulated energy when irradiated with excitation light such as a visible ray. Existence of the photostimulable phosphor was conventionally known. Radiography using the photostimulable phosphor is constructed as follows. That is, a radiation image of an object such as a human body is photographed and recorded on a sheet coated with the photostimulable phosphor. When the photostimulable phosphor sheet is scanned by excitation light such as a laser beam, photostimulated luminescence light is generated so that image data is obtained by photo-electrically reading the light. After the image data is suitably processed, an image represented by the image data is displayed on a display such as a CRT, or is printed on a film by a laser printer, etc. so that the radiation image can be displayed as a visible image.
Such radiography has performance equivalent to the conventional X-ray radiography in view of photographing sensitivity and image quality. For example, in comparison with the conventional X-ray radiography, an exposure area is very wide and a response of the photostimulated luminescence light to an exposure amount is approximately proportional to the exposure amount over the entire exposure area. Therefore, even when the object is photographed in any radiation amount, a luminescence area where the image exists can be grasped and normalized to be converted to a digital signal without under or over amounts. By combining the obtained signal with a suitable image processing method, an image of high quality can be steadily provided even under various kinds of photography condition. Further, since the obtained image is stored as image data, a large amount of image data can be stored for a long time period without causing deterioration of the image, and developments to a medical diagnostic information system, etc. can be realized.
FIG. 8 shows an example of a radiation image reading apparatus and a radiation image processing apparatus using the photostimulable phosphor sheet. A photostimulable phosphor sheet 31, on which a radiation image is recorded, is set to a predetermined position of the reading apparatus. The photostimulable phosphor sheet 31 is conveyed in Y-direction by a sheet conveying means 33 driven by a motor 32. On the other hand, a light beam (excitation light) 35 generated from a laser light source 34 is reflected and deflected by a rotary polygon mirror 37, which is driven by a motor 36 and rotated at high speed in an arrow direction, and passes through a convergent lens 38. Thereafter, an optical path of the light beam 35 is changed by a mirror 39, and the photostimulable phosphor sheet 31 is scanned by the light beam 35 in X-direction. By the scanning, photostimulated luminescence light 40 is generated from a part of the photostimulable phosphor sheet 31 irradiated by the light beam 35. A light amount of the photostimulated luminescence light 40 corresponds to radiation image information accumulated and recorded on the sheet. The photostimulated luminescence light 40 is guided by an optical guide 41, and is photo-electrically detected by a photomultiplier (multiplier phototube) 42. An analog signal output from the photomultiplier 42 is amplified by an amplifier 43, and is digitized by an A/D converter 44. The digital signal is transmitted as image data to an image processing apparatus 45.
In such a process of reading photostimulated luminescence light, there is also a case where “pre-reading” of the data is executed. The “pre-reading” is executed by scanning the photostimulable phosphor sheet 31 in advance by light beam at a low level to read an image recorded on the sheet schematically so that image data obtained by the pre-reading is analyzed. Thereafter, “main reading” is executed by irradiating a light beam at a level higher than that of the light beam irradiated in the pre-reading and scanning the sheet to read the image data in optimal reading condition according to a dosage of the irradiated radiation, etc.
The image processing apparatus 45 includes an input unit 46 having a keyboard or a mouse for inputting instructions or information, a driving unit 47 for operating a floppy disk, etc. as an auxiliary recording medium, a display 48 such as a CRT for displaying a visible image on the basis of the image data and a main body section 49 having a central processing unit (CPU), an internal memory, an interface for transmitting and receiving signals between the CPU and a hard disk as a recording medium, an image reading apparatus, and so on.
When the image data is received by the image processing apparatus 45, the received image data is analyzed and subjected to image processing such as normalization, gradation processing or logic reading processing. Then, the processed image is displayed on the display 48. Thereafter, processing of outputting the processed image on a film, etc. is executed by using a printer or the like and the output result is supplied for diagnosis.
The visible image obtained by the radiation image reading apparatus using the above-mentioned photostimulable phosphor sheet and the radiation image processing apparatus is normally printed on a film and is used in the medical diagnosis. At this time, various arrangements can be considered, such as an arrangement of recording one picture on one entire film, an arrangement of recording two pictures on one film in parallel with each other leftward and rightward or upward and downward, an arrangement of recording four pictures on one film and so on. In particular, in a case where it is desired to compare left-hand image with right-hand image as in mammography (breasts) or in a case where it is desired to observe front image and side image in parallel with each other as in the entire spine, a plurality of pictures are often displayed on one film, which will be called as a “multi-format output” hereinafter.
However, according to a conventional multi-format output, a plurality of pictures are output in a uniform format irrespective of kinds of the pictures. Therefore, clearances are formed between the plurality of pictures, which makes it difficult to compare the plurality of pictures with each other and to understand relation between the plurality of pictures.
Japanese patent application laid-open JP-A-3-287248 discloses a scoliosis diagnostic system for photo-electrically reading a radiation image of the spine recorded on the photostimulable phosphor sheet having a recording area corresponding to an entire length of the spine as an object to be photographed, executing image processing to reduce the read radiation image and outputting the reduced radiation image.
Further, Japanese patent application laid-open JP-A-8-294479 discloses a computer-supported image diagnostic apparatus. In the apparatus, an entire radiation image of an object is displayed, while local image data representing an image in a local area including a detected abnormal shading candidate is extracted from the entire image data. The image in the local area is displayed separately from the entire image on the basis of the local image data. The above-mentioned JP-A-8-294479 also discloses the following contents. In the case where X-ray images of breasts, etc. are to be displayed, an entire image of one breast and an entire image of the other breast are displayed simultaneously and adjacently back to back, for example. The local area including the abnormal shading candidate detected from the entire image data of the one breast, and a local area with respect to the same portion of the other breast are displayed in window areas arranged on the screen displaying the respective entire images so that corresponding portions of both two breasts can be directly compared and observed.
Further, Japanese patent application laid-open JP-A-9-238933 discloses a breast image display apparatus. In the case where pair images constructed by arranging a pair of left-hand and right-hand breast images back to back are displayed, the breast image display apparatus displays the selected one of a vertical direction pair image obtained by photographing the pair of left-hand and right-hand breasts from a vertical direction, a side direction pair image obtained by photographing the pair of breasts from a side direction, and a pair image with a local enlarged image partially including a local area enlarged image obtained by enlarging the local area including the abnormal shading candidate within the vertical direction pair image and the side direction pair image so as to improve observation and photograph reading performance.
However, at the actual scene of medical diagnosis, images are processed with respect to various objects by using the same apparatus. Therefore, it has been necessary for a user to select a format which conforms to each of the images every time when a portion of an object to be photographed such as the entire spine or the mammography is changed.